1. Field of the Invention
The present invention is directed to pin and collar type fasteners and is particularly concerned with an automated assembly for stringing fastener collars onto a magnetically centered mandrel.
2. Description of Prior Developments
U.S. patent application Ser. No. 599,184, incorporated herein be reference, discloses a method and apparatus for loading fastener collars into a fastener installation machine. The method includes the step of stringing individual fastener collars onto an elongated flexible mandrel that extends within a surrounding flexible tube.
Typically, the flexible mandrel and surrounding flexible tube will have a length of about twelve feet. The mandrel can have a diameter ranging from about one eighth inch up to about one half inch, depending on the size fastener collar being strung onto the mandrel. In order to string the annular fastener collars onto the flexible mandrel, the surrounding flexible tube may be suspended in a vertical position from a chute housing associated with a vibratory bowl type collar feeding apparatus.
The collars are sequentially fed from the feeding apparatus into the upper end of a chute. At this point, the collars are allowed to drop down through the chute onto the upper end of the mandrel which is located within the suspended flexible tube. A vacuum pump may be connected to the lower end of the suspended flexible tube to exert a vacuum force on the collars as they descend along the mandrel. The vacuum force helps to ensure a smooth downward flow of the collars along the mandrel, and a relatively tight packing of the collars along the mandrel surface.
Substantially the entire length of the flexible mandrel is utilized for stringing and holding the fastener collars. Each flexible mandrel will hold or support a relatively large number of fastener collars. For example, assuming a collar length of one half inch and a mandrel length of about twelve feet, a single flexible mandrel can serve as a stringer for over two hundred fastener collars.
In order to facilitate collar loading, the upper end of the flexible mandrel should be centered in the chute passage. Otherwise, a given fastener collar may have its end surface strike against the tip end of the mandrel so as to hang up or jam in the chute passage, i.e., not travel downwardly around and along the mandrel surface. Such jams are of course undesirable in that they cause temporary stoppage of the collar stringing process until the particular collar is removed from the chute structure. Centering of the flexible mandrel in the chute passage is made somewhat difficult because of the fact that the entire vertical length of the mandrel should be unconnected to the surrounding tube or chute structure in order to permit the annular fastener collars to freely pass downwardly along and around the mandrel surface.
Accordingly, a need exists for a mandrel centering device which coaxially aligns a mandrel within a chute without physical contact between the mandrel and chute.